This invention relates to a heat engine which uses acoustical traveling waves to cause expansion and contraction of a unit mass of motivating fluid.
It is well known that acoustical standing waves of considerable amplitude can be set up in a gas column by the application of heat at a suitable fixed point. The transformation of heat into acoustical standing waves is accomplished by the action of these standing waves in compressing, expanding, and moving the gas similar to that which is done in a more conventional heat engine by the pistons. The standing waves simultaneously compress and move the fluid through the heat source, then expand it while moving it in the reverse direction. For best operation, the heat exchange rate between heat source and the gas should be adjusted to provide a delay time of approximately one quarter of an acoustical period, so that on the average, the fluid is heated after the compression has taken place, but before the expansion. While standing wave heat engines have great appeal because of their lack of moving parts, the need for a thermal delay prohibits use of very good heat exchange and subsequent attainment of high efficiencies.